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Attempt To Replace Spark Gap By Thyristor In Marx Circuit N.Rishi P.S.Ponmurugavel Power systems-S.EEE sastra university thanjore, india [email protected] Power systems-S.EEE sastra university thanjore, india [email protected] Abstract—A Marx circuit is a type of electrical circuit first described by Erwin Marx in 1924, whose purpose is to generate a high voltage pulse. It is extensively used for simulating the effects of lightning in electrical equipment testing. In this paper we proposed an attempt to replace the spark gap used in Marx circuit by using thyristor. R.Dilip kumar Power systems-S.EEE sastra university thanjore, india [email protected] is applied only for a short time, solid state switches will not heat up extensively. Ac compensation for the higher voltages encountered, the later stages have to carry lower charge too. Stage cooling and capacitor re charging also go well together. Keywords-marx circuit,thyristors,spark gap,firing,overvoltage. I. INTRODUCTION A Marx generator is a clever way of charging a number of capacitors in parallel, then discharging them in series. When capacitors are fully charged, either the lowest gap is allowed to breakdown from over voltage or it is triggered by an external source (if the gap spacing is set greater than the charging voltage breakdown spacing). This effectively puts the bottom two capacitors in series, over voltage the next gap up and so forth. When using a spark gap configuration it is impossible to stop the discharging process. The discharge will continue until the capacitors are almost completely discharged, in simulation of lightning the time of interruption also important. It is impossible to produce a flat top pulse with a classic Marx generator circuit. To overcome this difficulty we proposed this scheme, it uses latest thyristor technology. The solid state technology was proposed in [3]. BJT was proposed [4]. In this proposed technology it is possible to generate more controllable Marx generator based on solid state switches also it can be called as thyristor Marx generator or controllable Marx generator. This will sacrifices some of the steep voltage edge offered by spark gap since the raising edge will be restricted by the solid state switches. II. REPLACEMENT OF SPARK GAP The Marx technique has been used to generate several kilo volts from a low charging source using solid state devices (thyristors) as switching device instead of spark gap. Particularly lower output voltages, the capacitors can be charged in parallel from a common source through a series inductor. The charging impedance has to withstand the full output voltage for the top stage. In solid state avalanche devices, a high voltage automatically leads to high current. Because the high voltage (a)Block diagram for replacement of spark gap The block diagram for replacement of spark gap is shown in figure (a). the inductance used in this proposed circuit is to oppose the rate of change of current. The capacitors are charged in parallel it is discharged in series by triggering the thyristor switch. The connections are to be made to change the series parallel combination vice versa. The circuit diagram is displayed in simulation and results i.e.) next section. The transformer used in this proposed method is reactive transformer. It is used to oppose the change current. This transformer has to be designed both coils on same core. The only application for mutual inductance in a dc system is where some means is available to switch power on/ off to coil induced voltage peaking at every pulse. The mutual inductance relation is given by Neumann formula M21=N1*N2*P21 Where, N1 is the number of turns in coil 1.N2 is the number of turns in coil 2. And p21 is the permeance of space occupied by flux. The arbitrary inductance M=K (L1L2)/2. Where K is the coupling co-efficient range between 0-1, L1 and L2 are the inductance of coil 1 and coil 2 respectively. III. SIMULATION AND RESULTS For simulating the proposed thyristor based Marx scheme we gave 5000 volts as input. This 5000v is produced using cockroft Walton voltage multiplier circuit. The input to the cockroft Walton voltage multiplier is 230v given using a 1:1 transformer. In the cockroft Walton multiplier circuit we build 22 stages. The basic cockroft Walton three stage in shown below fig.(b). Figure (d) simulation diagram for proposed scheme. Figure (b) model cockroft walton voltage multiplier circuit. The output of cockroft Walton voltage multiplier is shown in figure (c). The firing pulses are shown in figure (e). And corresponding output voltage for the proposed scheme is shown in figure (f) below. Input to this circuit is given from output of cockroft Walton voltage multiplier circuit i.e) 5000 volts dc. In this circuit diagram it is made to connect in parallel when charging. and the capacitors are connected in series when discharging by firing the thyristor. In the proposed scheme we got 20000 volts output as shown below. Figure(e) firing pulses to the thyristor switch Figure(c) output of cockroft Walton voltage multipler taken between last stage and ground. The input transformer is made of ratio 1:1. The output is that same of the input. The voltage output is higher in both of the circuits but the current is very less Simulation diagram for proposed thyristor based marx circuit is shown in figure (d). Figure (f) Output voltage of proposed marx circuit. IV. FUTURE WORK To design a thyristor to withstand for higher voltage up to desired level. For implementing as a practical circuit we need to use light activated thyristors. V. ACKNOWLEDGEMENT We thank Mr.S.Natarajan (A.P III)/S.EEE/Sastra university who guided us to present this paper. And we thank Mr.S.Mohmed ghouse for his kind co-operation. VI. CONCLUSION In this paper an attempt has been made to replace the spark gap by thyristors. Here we generate high voltage with low initial input by means of ideal thyristor switch which is used in high frequency application. For generating high voltage up to 160 kilo volts it is possible by increasing the number of stages and also by increasing the range of input and capacitor values. But the technical challenge is thyristor selection for very high voltage. REFERENCES [1] Lou van der Sluis, “transients in power systems”, John Wiley & Sons Ltd, 2001. L.m.Redondo,H.canasinnh and J.Fernando silva, “Generalised solid state marx modular topology,” IEEE Transaction, 2009 . [3] M.Inokuchi,M.akiyama, “development of miniature marxgenerator using BJT”,IEEE Transaction,2009. [4] Dongdong wang and“All solid state repetitive ulsed power generator using IGBT and magnetic compression switches”, IEEE transection, 2010 . [5] A.Carrus, D.Eng “Marx circuit modified by adding a tail sphere to generate lightning impulses lasting a few micro seconds,” IEEE Proceed. vol. 135, january 1985. [6] L.M.Redondo, M.T.Pereira, “Repetitive all solid state pulse marx type generator with energy recovery clamp circuit for inductive loads”. IEEE transaction,2007. [7] L.m.Redondo, H.canasinnh and J.Fernando silva, “New repetitive bi polar solid state marx type modulator”.IEEE Transaction,2008. [8] L.m.Redondo, J.Fernando silva, and A.fowler. “solid state marx type circuit for the isolate voltage target modulator” . [9] Archana sharma.v, S.Mitra, senthil. K, “Experimental results on design aspects of a compact repetitive marx generator”.IEEE Transaction.2009. [10] Yuan xulien, ding zhenjie, hao qing song, “high repetition and stability all solid state pulses based on avalanche transistor marx circuit”.proceeding ICMMT,IEEE transaction. [11] Zikang yang, lan xiong, xiaejie ye,bo long, “high voltage pulse generator based on marx circuit and it’s application for sterlization”. IEEE transaction. [2]